A known inkjet print head comprises a number of actuators operatively coupled to a fluid chamber for generating a pressure wave in a fluid present in the fluid chamber. The pressure wave results in a droplet of the fluid being expelled through an orifice, which orifice—commonly also referred to as a nozzle—is in fluid communication with the fluid chamber.
In a known inkjet printer, the print head is arranged on a carriage and the carriage scans along a recording substrate. Thus, the print head is arranged to expel droplets and provide a swath of dots of a recording substance, such as a fluid ink or a fluid etch resist, on the recording substrate in accordance with a predetermined pattern. Such a pattern may be a graphical image such as a photo or the like or may represent a functional pattern such as a pattern of an electrical circuit to be formed on a printed circuit board (hereinafter also referred to as PCB). After printing the swath, the recording substrate is moved relative to the print head over such a distance that the print head is enabled to provide a subsequent swath in addition to the previous swath. The predetermined pattern may thus be formed by a suitable number of adjacent or overlapping swaths
In another known inkjet printer, one or more inkjet print heads are fixedly arranged and the recording substrate moves relative to the one or more print heads, while the print heads expel droplets for forming the predetermined pattern in a single swath. In both above-described known inkjet printers, the print head and the recording substrate move relative to each other during printing, i.e. expelling of droplets, for forming the predetermined pattern. For forming the predetermined pattern, the droplets need to be positioned on the recording substrate accurately. If the resulting dots are not positioned accurately, the graphical image will show visible artifacts, which are undesirable. In case of a functional pattern, inaccurately positioned dots may lead to functional defects such as an interruption of an electrically conductive path, rendering the print result unusable. Consequently, it is at least desirable and in some instances even required that droplets are positioned accurately. At least one of the recording substrate and the print head moves during printing. For accurate positioning of dots it is needed that the movement is accurate, i.e. corresponds to an expected movement. In order to obtain an accurate movement, in a known printer, the movement is controlled to be uniform (constant velocity). However, it is virtually impossible or at least economically not feasible to actually obtain such a uniform movement in an inkjet printer. In practice, there are deviations from such uniform movement, for example due to manufacturing tolerances and the like. Therefore, it is known to determine the actual position of the moving part (recording substrate and/or print head) and use the determined actual position as a feedback signal in a control loop. In particular, the control loop is designed such that a deviation in the actual position as compared to an expected position is compensated by adapting the moment at which a droplet is expelled (hereinafter referred to as a droplet ejection moment). So, in the known printer, the control loop is designed to expel the droplet at such a moment that the dot will be positioned accurately.
In the known printer, however, droplet ejection is disturbed frequently, resulting in missing dots. It is evident that missing dots are at least undesirable and may even render the print result unusable, as above explained with respect to inaccurately positioned dots.